Who said you can't race a RTR T4? I race my T4 and it was a RTR, the only thing I did to it at the time was get a set of CVD's, and then later I got a set of turnbuckles (the steel ones are a little on the week side). Other then that it is still the same RTR that I bought when I first started (well execpt a few new parts here and there to keep it running nicely and to get rid of slop)
The Li-po should work fine with the ESC, only you will have to be sure not to discharge the battery too far as I am not sure if it has a li-op cut off or not.
As for the motor, they have a lot of power for a new racer, and I also know that they can keep up with some of the faster motors out there, only they will only last a few weeks at most before you need a new one (you can't cut the comm on them, other wise you would be fine)